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/****************************************************************************
**
** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** GNU Free Documentation License
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms
** and conditions contained in a signed written agreement between you
** and Nokia.
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qml-debugging.html
\ingroup qtquick-tools
\title Debugging QML
\brief debugging tools in QML
\section1 Console API
\section2 Log
\c console.log, console.debug, console.info, console.warn and console.error can be used to print
debugging information to the console. For example:
\code
function f(a, b) {
console.log("a is ", a, "b is ", b);
}
\endcode
The output is generated using the qDebug, qWarning, qCritical methods in C++
(see also http://doc.qt.nokia.com/latest/debug.html#warning-and-debugging-messages).
\hint Setting the environment variable QML_CONSOLE_EXTENDED also prints the source
code location of the call.
\section2 Assert
\c console.assert tests that an expression is true. If not, it will write an optional message
to the console and print the stack trace.
\qml
function f() {
var x = 12
console.assert(x == 12, "This will pass");
console.assert(x > 12, "This will fail");
}
\endqml
\section2 Timer
\c console.time and console.timeEnd log the time (in milliseconds) that was spent between
the calls. Both take a string argument that identifies the measurement. For example:
\code
function f() {
console.time("wholeFunction");
console.time("firstPart");
// first part
console.timeEnd("firstPart");
// second part
console.timeEnd("wholeFunction");
}
\endcode
\section2 Trace
\c console.trace prints the stack trace of JavaScript execution at the point where
it was called. The stack trace info contains function name, file name, line number
and column number. The stack trace is limited to last 10 stack frames.
\section2 Count
\c console.count prints the current number of times a particular piece of code has been executed,
along with a message. That is,
\qml
function f() {
console.count("f called");
}
\endqml
will print \c{f called: 1}, \c{f called: 2} ... whenever \c{f()} is executed.
\section2 Profile
\c console.profile turns on the QML and JavaScript profilers. Nested calls are not
supported and a warning will be printed to the console.
\c console.profileEnd turns off the QML and JavaScript profilers. Calling this function
without a previous call to console.profile will print a warning to the console. A
profiling client should have been attached before this call to receive and store the
profiling data. For example:
\code
function f() {
console.profile();
//Call some function that needs to be profiled.
//Ensure that a client is attached before ending
//the profiling session.
console.profileEnd();
}
\endcode
\section2 Exception
\c console.exception prints an error message together with the stack trace of JavaScript
execution at the point where it is called.
\section1 Debugging Transitions
When a transition doesn't look quite right, it can be helpful to view it in slow
motion to see what is happening more clearly. This functionality is supported
in the \l {QML Viewer} tool: to enable this,
click on the "Debugging" menu, then "Slow Down Animations".
\section1 Debugging module imports
The \c QML_IMPORT_TRACE environment variable can be set to enable debug output
from QML's import loading mechanisms.
For example, for a simple QML file like this:
\qml
import QtQuick 2.0
Rectangle { width: 100; height: 100 }
\endqml
If you set \c {QML_IMPORT_TRACE=1} before running the \l {QML Viewer}
(or your QML C++ application), you will see output similar to this:
\code
QQmlImportDatabase::addImportPath "/qt-sdk/imports"
QQmlImportDatabase::addImportPath "/qt-sdk/bin/QMLViewer.app/Contents/MacOS"
QQmlImportDatabase::addToImport 0x106237370 "." -1.-1 File as ""
QQmlImportDatabase::addToImport 0x106237370 "Qt" 4.7 Library as ""
QQmlImportDatabase::resolveType "Rectangle" = "QDeclarativeRectangle"
\endcode
\section1 Debugging with Qt Creator
\l{http://qt.nokia.com/products/developer-tools}{Qt Creator} provides built-in
support for QML debugging. QML projects and standalone C++ applications that
utilize QML can be debugged on desktops as well as on remote devices.
For more information, see the Qt Creator Manual.
*/
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